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Date:   Tue, 17 Mar 2020 05:53:58 -0300
From:   Bruno Meneguele <bmeneg@redhat.com>
To:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        pmladek@suse.com, sergey.senozhatsky@gmail.com, rostedt@goodmis.org
Subject: Re: [PATCH] kernel/printk: add kmsg SEEK_CUR handling
Message-ID: <20200317085358.GE11152@glitch>
References: <20200313003533.2203429-1-bmeneg@redhat.com>
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 <20200313110229.GI13406@glitch>
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On Tue, Mar 17, 2020 at 11:03:26AM +0900, Sergey Senozhatsky wrote:
> On (20/03/13 08:02), Bruno Meneguele wrote:
> > Ok, I poorly expressed the notion of "documentantion". The userspace
> > doesn't tell about returning -ESPIPE, but to the functions work properl=
y
> > they watch for -ESPIPE returning from the syscall. For instance, gblic
> > dprintf() implementation:
> >=20
> > dprintf:
> >   __vdprintf_internal:
> >     _IO_new_file_attach:
> >=20
> >   if (_IO_SEEKOFF (fp, (off64_t)0, _IO_seek_cur, _IOS_INPUT|_IOS_OUTPUT=
)
> >       =3D=3D _IO_pos_BAD && errno !=3D ESPIPE)
> >     return NULL;
> >=20
> > With that, if the seek fails, but return anything other than ESPIPE the
> > dprintf() will also fail returning -EINVAL to dprintf() caller. While i=
f
> > ESPIPE is returned, it's "ignored" and the call still works. The way we
> > have today make kmsg an exception case among the rest of the system
> > files where you can open with dprintf.
> >=20
> > One of the things I could agree with is removing the SEEK call from
> > dprintf, since fprintf basically follows the same steps, but doesn't
> > seek anything.  But at the same time, IMO it makes sense to make kmsg
> > interface complaint with the errno return values.
>=20
> The code in questions is very old. So let's add the missing bit to the
> kernel. At the same time, we probably can have a slightly more detailed
> documentation / code comment.
>=20
> =09-ss
>=20

Sure thing.

I'm going to send a v2 of this patch with more details still today or
tomorrow.

Thanks!

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